1. Field of the Invention
The present invention relates to a photosensitive composition that forms a polymer image by exposure to light, a photosensitive material comprising the photosensitive composition, and an image forming method which employs the photosensitive material comprising the photosensitive composition. More particularly it is concerned with a photosensitive composition which is highly sensitive and used to form a highly detailed polymer image using a silver halide as a photosensor, a photosensitive material comprising the composition, and with an image forming method using the photosensitive material.
2. Related Background Art
Energies used to form or record an image include light, sound, electricity, magnetism, heat, radiations such as electron rays and X-rays, and chemical energy. Among them, in particular, widely used are light, electricity, heat energy, or a combination of any of these.
For example, the image forming method that employs the combination of light energy with chemical energy includes a silver salt photographic process and a method in which a diazo copying paper is used. The method that employs the combination of light energy with electric energy includes an electrophotographic system. Also, the method that utilizes heat energy includes a method in which a heat-sensitive recording paper or transfer recording paper is used. On the other hand, known as the method that utilizes electric energy is a method in which an electrostatic recording paper, electrothermal recording paper, or electrosensitive recording paper is used.
Of the above image forming methods, the silver salt photographic process can obtain an image having a high resolution. The silver salt photographic process, however, requires the developing and fixing that uses complicated liquid compositions, or the drying treatment of an image (or a print).
Now, development is energetically made on image forming methods that can form an image through a simple processing,
For example, U.S. Pat. No. 4,629,676 teaches a method in which polymerization reaction under dry (thermal) conditions is caused by the photosensitive reaction of silver halide that acts as a trigger, to form an image comprising a polymer.
This method has the advantage that any complicated wet processings are not required, but has had the disadvantage that the polymer formation rate (i.e., polymerization rate of a polymeric compound) is so low that it takes a long time to form the polymer image. Incidentally, this disadvantage arises presumably because of a reaction intermediate (which functions as a polymerization initiator) formed in the course of heating, by the reaction between silver halide and a reduced agent in existence of silver catalyst produced by imagewise exposure, which intermediate is so stable and has so low activity as the polymerization initiator that the polymerization reaction can not proceed so rapidly.
On the other hand, for accelerating the polymerization to cope with this problem, Japanese Unexamined Patent Publication No. 62-70836 discloses a method in which a thermopolymerization initiator is used.
This method comprises forming a latent image comprising silver nuclei produced from silver halide by imagewise exposure, and converting, under heating, a reducing agent into an oxidized product having a polymerization inhibitory power different from that of said reducing agent by utilizing a catalytic action of the above silver nuclei, thereby producing a difference in the polymerization inhibitory power between the reducing agent and the resulting oxidized product and also causing a thermopolymerization reaction utilizing the thermopolymerization initiator, thus forming a polymer image according to the difference in the polymerization inhibitory power.
This method, however, has disadvantage that a good contrast can not be made in the polymer image.
This disadvantage arises presumably because the oxidation-reduction reaction taking place in a latent image portion to form the oxidized product and the polymerization reaction to form the polymer image are allowed to take place in the same heating step, so that these reactions may proceed in a competitive fashion and thus the respective reactions may not proceed with efficiency.
Also, the image formation according to this method is very unstable in that, for example, the areas on which the polymer is formed may turn into exposed areas or unexposed areas even by a slight change in the amount of the reducing agent.
In addition, U.S. Pat. No. 4,649,098 discloses a method in which a reducing agent having a polymerization inhibitory power is brought into an oxidized product by imagewise consumption (at exposed areas) in the course of the developing of silver halide, and at the same time, residual reducing agent enables imagewise inhibition (at unexposed areas) of polymerization reaction, and then light energy is uniformly applied, (whole areal exposure) from the outside to cause photopolymerization at the part which the reducing agent has been consumed, thus forming a polymer image.
The above method has the advantages that it can achieve a high sensitivity in the writing of a latent image since the silver halide is used, and the steps of from the writing for the formation of an image up to the whole areal exposure can be separated efficiency. It, however, is difficult to obtain a polymer image having a sufficient contrast.
More specifically, since the reducing agent used in the above method is in itself a reducing agent that acts as a polymerization initiator and does not to act as the polymerization initiator after the reduction of silver halide, it is necessary for obtaining an image having a good contrast to completely convert the reducing agent at the exposed areas into the oxidized product and also to impart the heat energy in a sufficient amount at the time of developing. However, excessive heating at high temperatures may cause an unintended oxidation-reduction reaction at the unexposed areas, reducing the contrast of the oxidation-reduction image, and eventually making worse the polymer image contrast. On the other hand, moderate heating at the time of developing may conversely not bring the oxidation-reduction reaction to sufficiently proceed at the exposed areas, so that not only the contrast becomes small but also the light energy required upon forming the polymer image must be applied in a sufficient amount. This may further cause an unintended polymerization at the unexposed areas, eventually making worse the polymer image contrast.
The polymer image to be formed according to the methods as described above is an image comprising a polymerized area and an unpolymerized area. For making this polymer image visible and further forming it into a color image, for example, U.S. Pat. No. 4,649,098 and so forth discloses various methods that utilize the difference in physical properties and so forth between the polymerized area and unpolymerized area. For example in one, proposed method in which a treatment is made using a liquid that does not dissolve the polymerized area and dissolves the layer of the unpolymerized area, thereby dissolving and removing the unpolymerized area (i.e., etching); another method which, utilizes the difference in adhesion between the polymerized area and unpolymerized area, a sheet such as plastic film is adhered and thereafter peeled to separate the polymerized area and unpolymerized area under dry conditions (i.e., peeling-apart); in the case where the polymer image is formed into a color image, a method in which a photopolymerizable layer is previously colored with use of a pigment or dye, which is then subjected to the above dissolving (i.e, etching) or peeling (i.e., peeling-apart) to form the color image, or a method in which, utilizing the adhesion at the unpolymerized area, a coloring powder is applied to make selective coloring (i.e., torning or inking), or, utilizing the difference in liquid-permeability between the polymerized area and unpolymerized area, the unpolymerized area is selectively dyed by treating it with a dye solution.
However, no polymer image having a sufficient contrast can be obtained in the conventional polymer image forming methods as discussed above, and hence, even with employment of any of the above methods for making the image visible or forming it into a color image, the visible image and color image which are obtained from such a polymer image can not have any sufficient contrast, and particularly it has been difficult to obtain highly detailed visible image and color image.